Numerous variants of so-called internal mixers, kneaders or Banbury mixers have been disclosed. Basically they are batch-wise operated mixers with a mixing chamber comprising two cylindrical partial mixing chambers overlapping each other in part. A mixing shaft with one or several kneading blades is arranged in each partial mixing chamber. These blades may mesh or rotate one past the other. The blades are driven to rotate in opposite directions. Mixing material is supplied from above through a feed shaft to be closed by means of a stamp arranged in the vicinity of the upper saddle of the mixing chamber. A discharge opening is provided in the vicinity of the lower saddle of the mixing chamber. Such mixers are for instance known from U.S. Pat. No. 4 058 296, from U.S. Pat. No. 4 234 259 or from DE 20 59 844 A (corresponding to U.S. Ser. No. 882 560 of Dec. 5, 1969). Such internal mixers are preferably used to knead caoutchouc and to include fillers and additives into caoutchouc. But they can also be used for a plurality of other mixing and kneading objects. The melting of thermoplastics in the internal mixer, as it occurs for the manufacture of thermoplastic elastomers or cable compounds during mixing with caoutchouc, is extraordinarily time-consuming. It is even more difficult if not impossible to manufacture highly loaded compounds, in which the fillers are not to be damaged if possible, so that they are supplied to the mixer only after the basic material is completely melted. If internal mixers are used to this effect, this means that the mixer is filled only to some minor degree when the thermoplastics are first supplied in the form of granules, grit or powder. The power supply to the thermoplastic is extraordinarily small with the consequence that the melting process takes an extremely long time or does not take place at all, the more so as for structural reasons the width of the gap between the blades and the wall of the mixing chamber is as a rule comparatively large, by all means larger than the grain diameter of thermoplastic in the form of grit or powder. As a rule this also applies to the grain size of granules in comparison to the gap widths between the kneading blades and the wall of the mixing chamber. Even if the grain size of the granules is larger than the gap, the granules will mostly roll along the kneading blades and will not be sheared in the gap, until they are sufficiently heated to stick to the wall of the mixing chamber or the kneading blades.
It has further been disclosed to inject oils directly into the mixing chamber of internal mixers by way of an injection nozzle.